EP1274761B1 - Method and device for producing granulates from intermediate products of thermoplastic polyesters and copolyesters - Google Patents

Abstract

The invention relates to a process and an apparatus for forming molten drops of precursors of thermoplastic polyesters or copolyesters as molten monomer, oligomer, monomer/glycol mixture or after partial polycondensator [sic] and melting to give a molten precursor, in which the precursor formed into drops is introduced into a gaseous medium, and the gaseous medium, after entry of the precursor formed into drops into the gaseous medium, accelerates the crystallization process by holding the drop-form precursor at a temperature above 100° C. and below its melting point for a limited time until crystallization of the drop at the surface of the precursor is complete. To this end, the apparatus has a fall tower, through which the gaseous medium flows in countercurrent from bottom to top, while the drops fall in the vertical direction from top to bottom into a collecting funnel with a precrystallized surface.

Description

The invention relates to a method for dropletizing preliminary products thermoplastic polyester or copolyester as a molten monomer, Oligomer, monomer-glycol mixture or after a partial Polycondensation and melting into a molten intermediate product, whereby the dripped preliminary product is introduced into a gaseous medium, and an apparatus for performing this method.

From the document US 4,436,782 is a process for granulation and Further treatment of a polyethylene terephthalate (called PET) into pellets known, a formed at temperatures between 260 and 280 ° C. liquid oligomer with a viscosity number (or intrinsic viscosity) between 0.08 and 0.15 is pressed through nozzles such that drops arise through a cooling area inert gas atmosphere in a water bath drop to solidify the drops into amorphous pellets. From this Document is also known that a drum instead of a water bath or a conveyor belt can catch the drops to make them amorphous Let the pellets cool and solidify.

The method has the disadvantage that in the liquid provided, namely Water, or on the intended conveyor belt a solidification of weak polycondensed polyester such as polyethylene terephthalate, amorphous pellets as preliminary products, which are only energetically and by another economically complex step implemented in crystalline precursors Need to become. Because these precursors when converted to crystalline Intermediate products and a sticky phase in higher polymer substances can undergo further treatment and polycondensation of the pellets can only be made in complex designed fluidized bed ovens sticking of the pellets during crystallization and more To prevent polycondensation.

Different granulation processes to make amorphous polyester pellets Producing crystalline pellets are known from US Pat. No. 5,540,868. To do this the amorphous polyester intermediate is heated to temperatures above 70 ° C, to trigger the crystallization process. But has amorphous polyester Temperatures above 70 ° C have the disadvantage that it is a sticky surface having. To stick or clump the amorphous polyester To prevent crystallization temperatures above 70 ° C, the intermediate must be Granules are present and can then in a fluidized bed reactor Corresponding hot gas flows are kept in motion until in one process lasting several hours, at least the surface has crystallized to the extent that sticking of the preliminary products is excluded.

While amorphous polyester is transparent, the crystalline phase is one Intermediate product of a polyester or copolyester on white coloring clearly visible. It is usually used to overcome stickiness of amorphous polymer the crystallization process of the precursors with the further reinforced polycondensation, which is usually between 200 and 230 ° C is carried out in a fluidized bed reactor. This will the reactor operated in such a way that initially to overcome the stickiness crystallization at an optimal crystallization temperature at about 150 ° C for several hours and then the pellets or Granules for additional hours to higher chain lengths at temperatures be condensed between 200 and 230 ° C.

From the same above publication (US 5,540,868) it is known that the Crystallization of pellets can also be triggered by a thermal shock, by hitting hot pellets on a cold surface or vice versa Pound amorphous pellets on a hot surface. Such one Shock crystallization has the disadvantage that reproduction is extremely difficult is because the temperature of a hot plate is between 300 and 800 ° C in Vary depending on how long the pellets stay on the plate. at Rotary plates are used in the temperature range between 30 and 200 ° C, which in turn depends on how long the pellets stay on the hot rotary plates. In addition to the purely thermal problems, which are in such a process for crystallizing the pellets considerable mechanical problems have to be overcome.

The object of the invention is a method and an apparatus for Dripping of intermediate products of thermoplastic polyester and copolyester according to the preamble of claim 1 and claim 14 specify which overcomes the disadvantages in the prior art, a Process shortening of conventional granulation processes causes and on builds previously known method steps and devices to at least surface crystallized dropletized precursors in the form of Monomers, oligomers, monomer-glycol mixtures or partially to produce polycondensed materials.

This task is carried out with the characteristics of the subject of the independent Claims resolved. Advantageous further developments of the invention result from the dependent claims.

For this purpose, according to the invention, the preliminary product is converted into a gaseous medium introduced, the gaseous medium after the entry of the droplet Preproduct in the gaseous medium the crystallization process Pre-product accelerates and the state of crystallization of the pre-product accelerated by placing the dripped intermediate product on a Temperature above 100 ° C and below its melting point for a limited Period of time until crystallization of the drop in the surface of the Intermediate product is completed.

This solution has the advantage that by using this gaseous Medium the drop-shaped intermediate product at a temperature above 100 ° C. and is kept below its melting point, for a limited one Time so that crystallization nuclei in the form of defects due to the high surface temperature of over 100 ° C, which with increasing Release of the heat of fusion of the drop from near-surface germs Cause crystallization of the surface in the limited period so that the drop-shaped preliminary product as spheres with pre-crystallized and thus non-stick surface after passing through a drop distance can be caught without sticking, and thus for one Immediate further treatment to high polymer polycondensate used can be. This makes the long conventional one advantageous Preparation phase avoided in a fluidized bed reactor in which, as above mentioned, first the amorphous state of the pellets via a sticky phase in the pellets can be overcome within several hours.

In a preferred embodiment of the method, the gaseous medium is Air. Air can be used for some types of monomers, oligomers or partially polycondensed precursors due to their oxygen content Formation of crystal nuclei contribute, however, for many the Polycondensates and their monomers when dropletized are low in oxygen Atmosphere can be made available, especially at low viscosity PET an oxidative damage during the Crystallization process can occur. In a preferred embodiment The process therefore ensures a low-oxygen atmosphere that such damage does not occur.

In a further preferred implementation of the method, an inert gas is used. An inert gas then becomes Required if precursors of polyesters or copolyesters drip that are particularly sensitive to different gas atmospheres react, so that here the nuclei only by the Maintaining a high temperature, namely generated above 100 ° C, in that a as a seed on the surface of the drops sufficient density of vacancies and thermal defects becomes.

Nitrogen can advantageously be used as a further gaseous medium the nitrogen used in many of the preliminary products to be dripped shows no chemical reactions and therefore a quasi-inert environment delivers and thus only the high temperature of the gaseous medium Nitrogen ensures the formation of nuclei.

The gaseous medium is preferably countercurrent to one Falling distance of the dripped preliminary product led and warms up at Rise of the gas along the fall path so that it is ensured that the dripped intermediate product for a limited period of time, namely during it the falling distance against the gaseous medium passes through Maintains temperature above 100 ° C. Because the melting drop itself is above 200 ° C is hot, it heats the counter-flowing gas and heats it up so that when the gas is circulated, the heated gas of the falling section can be supplied again and possibly the heated gas energy must be withdrawn for a temperature above the limited period Do not unnecessarily enlarge 100 ° C for the dripped preliminary product while too At the beginning of the dropletization process, the gaseous medium is to be heated to make it available tempered.

To generate the counterflow, the gaseous medium is injected into the Falling distance of the dripped preliminary product preferably at the lowest level of the falling distance and tempered beforehand. The tempering takes place preferably by means of a heat exchanger, each of the gaseous medium cools or heats as needed so that it remains constant Temperature as a countercurrent into the falling section of the dripped preliminary product can be introduced.

The insertion temperature is greater than or equal to 30 ° C and less 120 ° C regulated, preferably temperatures greater than or equal to 40 ° C and maintained below 100 ° C. These partially low Inlet temperatures ensure that the dripped intermediate products at a temperature above 100 ° C during the Traversing the falling distance can be kept.

The preliminary products are in a further embodiment of the invention melted down due to vibration excitation. Here are the Vibration excitation at a frequency between 30 and 1,000 Hz, preferably between 50 and 400 Hz. A throughput of 5,000 up to 30,000 kg / h can be achieved. This throughput can be achieved by a flat Distribution of nozzles on a nozzle head plate still significantly increased become. For this purpose, the nozzle head in a preferred embodiment of the Process the intermediate product with an intrinsic viscosity in the range fed between 0.05 to 0.3 dl / g. With a given nozzle diameter the drop diameter increases and increases with increasing viscosity increasing frequency. In this respect, the diameter of the drops is one Vibration-induced droplets are relatively accurate over the Melt temperature (setting the intrinsic viscosity) and the Vibration frequency adjustable.

The melting point of a PET monomer is 230 to 240 ° C and is therefore lower than the final PET polymer. The freezing point of the Dropped preliminary product can be assumed to be around 200 ° C, so that after the appearance of the drop from the nozzle and a short drop distance until the solidification point of about 200 ° C is reached, none at first Crystallization occurs and in the further cooling phase of the drop initially Crystal nuclei are formed on the surface as long as the drops are over Can be kept 100 ° C, the crystal nuclei essentially Defects and empty spaces arise. One of the crystal seeds then goes out Crystallization of the droplet surface, which ultimately ensures that the Drops at the end of the fall no longer have any sticky properties, as would be the case with amorphous pellets above 70 ° C. For this Crystallization phase in a gaseous countercurrent in which the drop the preliminary product is kept above 100 ° C, has a fall height of 8 to 15 m, depending on the diameter of the drop. So is an essential one Parameters of the process the reproducibility and the uniformity of the Droplet diameter.

In a preferred implementation of the method, the preliminary product is added Droplets whose diameter is more than 80% by weight in the range of twice the nozzle diameter, and a diameter below the Nozzle diameter less than 3 wt .-% and a diameter larger than three times the nozzle diameter to less than 10 wt .-% of dripped intermediate product occurs. With this high uniformity of Dripping of the vibration-excited melt of an intermediate product Polyesters or copolyesters are the advantages of a uniform Crystallization, a uniform cooling and an achievable low tendency of the drops to adhere.

This narrow ball size division also provides a small amount of dust, which at the method according to the invention is less than 1%, with which the The advantage of a reduced electrostatic charge, a lower one Amount of rejects and a reduced risk of explosion. Finally, in further processing in solid state polycondensation (Called SSP) a narrow grain size spectrum, as with the method according to the invention is possible for a more uniform Ensure polycondensation. A ball size of approximately 0.5 to 2 mm in diameter significantly accelerates the condensation of water and glycol in the Further treatment in the course of solid state polycondensation. There is one Ball size of 1 to 10 mg a significant improvement over the previous one used granulate sizes that are significantly higher.

Finally, it is of particular advantage if as a preliminary product Precrystallized monomer drops can be used because the subsequent further processing less unwanted intermediate or Fission products arise than with conventional processing methods.

einen Düsenkopf, der durch Schwingungsanregung der Schmelze tropfenförmige Pellets aus dem Vorprodukt bildet,

einen Fallturm, in dem das vertropfte Vorprodukt im Gegenstrom eines gasförmigen Mediums temperiert wird,

einen Wärmetauscher, der im Bodenbereich des Fallturms angeordnet ist und das gasförmige Medium aufheizt oder kühlt, um es auf gleichmäßig hohe Einströmtemperatur zu regeln,

ein Gebläse, welches das gasförmige Medium im Fallturm auf eine vorgegebene Strömungsgeschwindigkeit beschleunigt, und

eine Rückführleitung, die das gasförmige Medium nach Verlassen des Fallturms zum Wärmetauscher zurückführt.

A device for carrying out the dripping process has the following features:

a nozzle head which forms drop-shaped pellets from the preliminary product due to vibration excitation of the melt,

a drop tower in which the dripped preliminary product is tempered in countercurrent to a gaseous medium,

a heat exchanger, which is arranged in the bottom area of the drop tower and heats or cools the gaseous medium in order to regulate it to a uniformly high inflow temperature,

a blower which accelerates the gaseous medium in the drop tower to a predetermined flow rate, and

a return line that returns the gaseous medium to the heat exchanger after leaving the drop tower.

On the one hand, this system has the advantage of being relatively uniform Dropletization of the molten preliminary product due to vibration excitation, on the other hand, the advantage of the relatively simple structure, which is only one provides sufficient fall distance in a drop tower to a limited residence time of the dripped intermediate in a temperature above To ensure 100 ° C, taking the heat energy from the dripped Upstream product is released to the counter-flowing gas, is used to to be reused to save energy. By the length of the drop distance and the preheating or tempering temperature of the introduced gaseous Medium can dwell time above the critical 100 ° C in the falling distance of the drop tower. Overall determine vibration frequency the dropletizer, nozzle diameter of the nozzle head, viscosity and thus temperature of the preliminary product in the nozzle head and temperature control of the gaseous medium the diameter and the crystallization progress of the dripped intermediate product. The degree of crystallization can be roughly above that milky cloudiness of the drip can be determined, so that here too reliable sample check of the functioning of the device and the procedure is feasible.

In a preferred embodiment of the device for performing the The method of the nozzle head has nozzle openings which prevent droplets from forming secure in the vertical direction. The vertical droplet creates in Contrary to a spray nozzle the possibility of dropping the drop run completely parallel without touching the wall through the drop tower of the system and according to the specified drop distance, which corresponds to a crystallization time, the granules or the spherical drops stick-free in a funnel to catch and lead out at the bottom of the drop tower.

In a further preferred embodiment of the invention, the Heat exchanger the temperature of the gaseous medium to one Insertion temperature greater than or equal to 30 ° C and less than or equal to 100 ° C, preferably regulated greater than or equal to 40 ° C and less than or equal to 100 ° C. To A heat exchanger fluid flows through the heat exchanger separately regulated and temperature-stabilized circuit, so that the heat exchanger the circulated gaseous medium automatically cools down The insertion temperature is exceeded and automatically warmed or heated if the set insertion temperature or the temperature falls below of the heat exchanger fluid.

In a further preferred embodiment of the invention, a Flow rate from 0.3 to 1 m / s of the gaseous medium in the Drop tower set via a blower. The blower can be in the floor area or be arranged behind the heat exchanger and as a pressure fan Generate counterflow of the gaseous medium in the drop tower or it can as Suction fan to be designed and after the outlet opening for gaseous Medium of the plant in the area of the dripping area around the Nozzle head must be positioned.

The drop distance in the drop tower is in a preferred embodiment Invention 10 to 20 m long, preferably 12 to 15 m, so that a limited An optimal crystallization time of 2.5 to 3.5 s was observed can be.

example 1

A monomer-glycol mixture of a polyethylene terephthalate with a Viscosity number or an intrinsic viscosity of 0.2 is with a Temperature of about 260 ° C through a nozzle head for droplets and Melt discharged, the nozzle diameter is 0.75 mm, so that the emerging melt of the intermediate of a polyester Vibration excitation to drops with a diameter of about 1.5 mm is dripped. These essentially spherical drops pass through Falling distance of approx. 15 m, during which it is gaseous using a low-oxygen Medium are kept at a temperature above 100 ° C. During this limited fall time of approx. 3 s due to the limited fall distance the surface of the drops of crystallization nuclei and crystallize the Surface such that no sticky amorphous state when passing through Temperatures below 100 ° C occurs. On the fall of the drop tower of one At a height of around 15 m, the granules crystallized on the surface cool a processing temperature of about 70 ° C and is in one Funnel collected at the bottom of the drop line. A DSC measurement (or Dynamic Scanning Calometry) gives a degree of surface crystallization of 100% for the resulting spherical granules, which on average have a Have a diameter of 1.5 mm, with over 80% of the dropped The intermediate product is in the range of twice the nozzle diameter and fall less than 3% by weight below the diameter of the nozzle diameter and less than 10% by weight over three times the nozzle diameter lie. With this narrow sphere size distribution of less than 3% of the Balls with a diameter smaller than the nozzle bore and less than 10% of the balls with a diameter larger than three times Nozzle bore diameter will advantageously be uniform Material quality through uniform cooling conditions and a uniform material quality due to uniform crystallization conditions achieved, from which a uniform and low adhesion tendency of the dripped balls results. Furthermore, this has low and narrow Ball size distribution the advantage of a uniform material quality the subsequent processing. In solid polycondensation Condition, the so-called SSP process, prevail evenly Conditions, and thus a material is achieved with a relative homogeneous molecular weight of the polycondensation chains. Moreover this narrow ball size distribution ensures an extremely small proportion of fine or dust material, which is less than 1%, so that less waste arises and a low electrostatic charge in the area of the drop tower occurs, so that the area of the drop tower is protected from a dust explosion is.

Example 2

If a polyester precursor drips with an intrinsic Viscosity that falls below 0.15 can reduce the fall time to no superficial crystallization in the drop tower of the embodiment are sufficient so that drops from a melt with low viscosity may remain sticky and thus clog the collecting funnel. In this The droplets with fine polyester particles fall into the droplet area covered in the surface, on the one hand, through the crystallization process to accelerate corresponding crystallization nuclei and on the other hand that Material when hitting a collecting funnel after passing through the To protect the drop tower from sticking. With this embodiment it is possible to use low-viscosity precursors of polyesters and copolyesters even with shorter drops in the dripped state before sticking to protect. The feeding with fine polyester particles can be done in one another preferred embodiment of the invention with the Inlet opening for gaseous medium in counterflow from the floor area of the drop tower and the polyester particles can, as far they are not required for coating the drops over the Outlet opening for gaseous medium are discharged from the system, so that it is ensured that there is no explosive dust mixture in the drop tower accumulates.

The invention will now be explained in more detail with reference to FIG. 1.

Figure 1 shows an apparatus for performing a method for Dripping of intermediate products of thermoplastic polyester or copolyester. For this purpose, the device has a nozzle head 1 which passes through Vibration excitation of the melt 2 by means of a vibration generator 14 forms drop-shaped pellets 3 from the preliminary product. The preliminary product is called Melt 2 of a monomer, an oligomer, a monomer-glycol mixture or a partially polycondensed preliminary product via the Melting device 15 fed to the nozzle head 1. The dripping unit 19, which is installed in the uppermost area of the plant, the following Head area 20 is able with these auxiliary devices to a low-viscosity melt to the nozzle head 1 via the melt line 21 feed and through the vertically downward nozzle openings 8th vertical drop.

The device also has a drop tower 4, which is below the Head area is attached and has a length of 10 to 20 m and thus provides a fall path 9 for the spherical drops, which essentially consists of the height of the drop tower 4 and a drop distance in the head region 20 in the embodiment according to FIG. 1. in the Bottom area 22 of the drop tower 4 is a filling area 23 in which a collecting funnel on the surface as it traverses the fall path 9 crystallized spherical drops can be collected and in Filling area portioned or forwarded for further processing can.

In the foot area 22 of the drop tower 4 there is an entry opening 11 for a Gaseous medium arranged between an annular opening 24 between Drop tower end 25 and collecting funnel 10 is arranged and the fan 6 via the heat exchanger 5 and the return line 7 of the inlet opening is fed. The ring opening 24 at the drop tower end 25 ensures one uniform counterflow of the gaseous medium from the foot region 22 of the Drop tower 4 to outlet openings 12 for the gaseous medium in the Head region 20 of the device. A return line 7 to the Entry opening 11 is connected downstream of the exit openings 12, so that the gaseous medium can be circulated.

The composition of the gaseous medium is the material of the adapted pre-dripped product and can vary depending on the sensitivity against oxygen air, oxygen-poor air, essentially nitrogen or be an inert gas, which is opposite to the direction of the drops in the drop tower rises at a speed between 0.3 to 1 m / s. In one The embodiment is the flow rate of the gaseous Medium 0.6 m / s. The gaseous medium is in this system with the help of Heat exchanger 5 preheated to a constant temperature as required, which in the foot area 22 of the drop tower 4 with a sensor 18 for the Inlet temperature of the gaseous medium is detected. The recorded value is fed to a control unit 13 which contains a fluid for the heat exchanger a heating and cooling device at a predetermined temperature that is monitored via a temperature sensor 17 for the heat exchanger fluid, so that the controller 13 using the temperature of the heat exchange fluid the heating and cooling device 16 can regulate. The control unit 13 can continue via the connection point A to the vibration generator 14 act and the oscillation frequency, which is in the range of 30 Hz to 1 kHz is adjustable, change. Furthermore, the control unit 13 can Affect connection point B on the melting device 15, on the one hand the viscosity of the melt through the melting temperature of the Melting device 15 is controlled and on the other hand, the mass flow over a corresponding pressure supply in the melting device 15 is influenced can be.

With the control of the pressure and the temperature of the melt can At the same time the diameter of the drops can be changed, which is optimal about 80% by weight twice the diameter of the nozzle openings 8 corresponds and is only 3% below the diameter of the nozzle opening 8 and less than 10% by weight three times the diameter of the nozzle opening 8 equivalent. An optimal diameter size has been found for both 1.5mm the generation of pre-crystallized, i.e. crystallized on the surface Drop of the preliminary product, as well as for the further processing of the Pre-product to long-chain polyesters and copolyesters as optimal proved.

In this embodiment, the control device 13 is microprocessor-controlled and is suitable for regulating both the inlet temperature of the gaseous medium, as well as the throughput of the gaseous medium and the throughput of the to control the droplets of a polyester and / or copolyester. This ensures that the falling distance 9 from the nozzle head escaping melting drops at a temperature of 240 to 290 ° C heated melt to a solidification temperature around 200 ° C in Head area 20 of the device can be cooled and tempered by the temperature gaseous countercurrent for a period of 2.5 to 3.5 s on one Temperature be kept above 100 ° C, so that on the surface of the When solidifying, drops form seed crystals that form one Compact the near-surface crystallization layer until the drops are covered with a Temperature below 100 ° C in the foot area 22 of the drop tower through the Collecting funnel 10 are collected and discharged. To improve the Energy balance of the device is the drop tower 4 and the foot area of the Fallturm 4 heat-insulating and the gaseous medium is in a circular process for partial recovery of the heat of fusion.

LIST OF REFERENCE NUMBERS

1

nozzle head

2

melt

3

pellets

4

Fallturm

5

heat exchangers

6

fan

7

Return line

8th

nozzle opening

9

fall distance

10

receiving hopper

11

Inlet opening for gaseous medium

12

Outlet opening for gaseous medium

13

control unit

14

vibration generator

15

melting device

16

Heating and cooling device

17

Temperature sensor for heat exchanger fluid

18

Temperature sensor for inlet temperature of the gaseous medium

19

Vertropfungseinheit

20

head area

21

melting line

22

footer

23

filling area

24

ring opening

25

Fallturm end

Claims (18)

1. Process for forming drops of precursors of thermoplastic polyesters or copolyesters as molten monomer, oligomer, monomer/glycol mixture or after partial polycondensation and melting to give a molten precursor, wherein the precursor formed into drops is introduced into a gaseous medium, characterized in that the gaseous medium, after entry of the precursor formed into drops having a diameter of from 0.3 to 3 mm into the gaseous medium, accelerates the crystallization process of the precursor and brings about the crystallization state of the precursor in an accelerated manner by holding the drop-form precursor at a temperature above 100°C and below its melting point for a limited time until crystallization of the drop at the surface of the precursor is complete.
2. Process according to Claim 1, characterized in that the gaseous medium employed is air.
3. Process according to Claim 1, characterized in that the gaseous medium employed is a low-oxygen atmosphere.
4. Process according to Claim 1, characterized in that the gaseous medium employed is an inert gas.
5. Process according to Claim 1, characterized in that the gaseous medium employed is essentially nitrogen.
6. Process according to one of the preceding claims, characterized in that the gaseous medium is passed in countercurrent to a fall zone of the precursor formed into drops.
7. Process according to Claim 6, characterized in that the gaseous medium is introduced under temperature control into the fall zone of the precursor formed into drops at the lowest level of the fall zone.
8. Process according to Claim 7, characterized in that the temperature control of the gaseous medium takes place by means of a heat exchanger, and the gaseous medium is circulated.
9. Process according to one of the preceding claims, characterized in that the precursor in molten form is formed into drops by vibration excitation.
10. Process according to one of the preceding claims, characterized in that the precursor having an intrinsic viscosity in the range from 0.05 to 0.3 dl/g is formed into drops.
11. Process according to one of the preceding claims, characterized in that the precursor is formed into drops whose diameter is to the extent of greater than 80% by weight in the region of twice the nozzle diameter, and a diameter less than the nozzle diameter occurs to the extent of less than 3% by weight and a diameter greater than three times the nozzle diameter occurs to the extent of less than 10% by weight of the precursor formed into drops.
12. Process according to one of the preceding claims, characterized in that a dust-particle content of less than 1% by weight of the precursor formed into drops occurs during drop formation.
13. Process according to one of the preceding claims, characterized in that a low-viscosity precursor having an intrinsic viscosity of less than 0.15 is formed into drops in an environment with fine polyester particles, resulting in coating of the drops at the surface with polyester particles, which promotes crystallization and prevents the solidified drops from sticking together.
14. Apparatus for carrying out the process according to one of Claims 1 to 14, said apparatus comprising:

    a nozzle head (1) which forms drop-form pellets (3) from the precursor by vibration excitation of the melt (2),

    a fall tower (4), in which the temperature of the precursor formed into drops can be controlled in a countercurrent of the gaseous medium,

    a heat exchanger (5), which is arranged in the base region of the fall tower (4) and heats or cools the gaseous medium in order to regulate it to a uniformly high inflow temperature,

    a fan (6), which accelerates the gaseous medium in the fall tower (4) to a given flow rate, and

    a return line (7), which feeds the gaseous medium to the heat exchanger (5) after leaving the fall tower (4).
15. Apparatus according to Claim 14, characterized in that the nozzle head (1) has nozzle apertures (8) which are vertically facing and ensure drop formation in the vertical direction by means of vibration excitation of the melt (2).
16. Apparatus according to Claim 14 or 15, characterized in that the heat exchanger (5) regulates the temperature of the gaseous medium to a feed temperature of greater than or equal to 30°C and less than or equal to 120°C, preferably greater than or equal to 40°C and less than or equal to 100°C.
17. Apparatus according to one of Claims 14 to 16, characterized in that the fan (6) can be adjusted to a flow rate of from 0.3 to 1 m/s of the gaseous medium in the fall tower (4).
18. Apparatus according to one of Claims 14 to 17, characterized in that the fall tower (4) has a fall zone (9) of from 10 to 20 m, preferably from 12 to 15 m, for the precursor formed into drops.

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